The invention relates to a method for joining together two extremely thin metal sheets or metal foils which are at least partly superimposed on one another, eg. at the margins, and also to an apparatus for performing such a method of joining.
"Extremely thin metal sheets and foils" (hereinafter called "metal foils") are self-supporting, flexible sheets with thicknesses of between 2 .mu.m and 0.2 mm, and in particular between 20 .mu.m and 0.1 mm, consisting for example of stainless austenitic or ferritic materials. Their small thickness makes it difficult to join two metal foils together. This especially applies where the joint is to be made by a weld seam.
For joining together two metal foils which are superimposed one on the other, resistance roller seam welding is a known process. In the roller seam welding process the metal foils to be joined together are passed between two rollers through which an electric current, preferably an alternating current, is flowing. The flow of current through the two foils between the two welding rollers causes fusion of the area of contact of the two foils, forming a weld seam which joins the foils together. This weald seam usually consists of a succession of individual weld nuggets of a size which, if the weld seam is correctly formed, is in a certain proportion to the thickness of the metal foil and to the width of the weld. However, because the foils are very thin, it frequently happens that the weld nuggets penetrate right through to the surfaces of the sheets, thus greatly impairing the quality of the weld, or rendering it completely unusable. For these reasons, roller seam welding of metal foils is carried out at a speed below 2 m per minute, which is exceptionally slow for large-scale production, with the result that the costs of roller seam welding of metal foils are too high, and therefore uneconomic.